class Solution {
public:
    int canCompleteCircuit(vector<int>& gas, vector<int>& cost) {
        int n=gas.size();
        for(int i=0;i<n;i++)
        {
            int rest=0;
            int step=0;
            for( ;step<n;step++)
            {
                int index=(i+step)%n;
                rest=rest+gas[index]-cost[index];
                if(rest<0) break;
            }
            if(rest>=0) return i;
            i=i+step;
        }
        return -1;
    }
};
